Intermediate Toxicity Research Articles

Enhanced removal of bisphenol A by cyclodextrin in photocatalytic systems: Degradation intermediates and toxicity evaluation

At present, the assessment of photooxidation system mainly focuses on the photodegradation efficiency of target pollutant, lacking of the toxicity assessment in the photocatalysis process. Here, photodecomposition of bisphenol A (BPA) was used to investigate the performance of several cyclodextrin modified photocatalysts. Moreover, the comprehensive toxicity changes of BPA under different photocatalytic oxidation conditions were conducted. The β-cyclodextrin (β-CD) modified photocatalyst, including titanium dioxide (CM-β-CD-TiO2), carbon nitride (CM-β-CD-C3N4) and cadmium sulfide (SH-β-CD-AM/CdS) exhibit high degradation rate and mineralization efficiency of BPA. The highest total organic carbon (TOC) removal of BPA observed in the oxidation system of SH-β-CD-AM/CdS nanoreactor (73.4%). The main oxidation intermediates in these systems were detected, and the comprehension toxicity of BPA and its oxidation intermediates in different system were compared by toxicity estimation software tool (T.E.S.T.) based on quantitative structure-activity relationship (QSAR) prediction. The results show that β-CD can facilitate the photodecomposition of the target contaminant. However, many oxidation intermediates with high comprehensive toxicity, even in the oxidation system with high BPA removal, can still be detected. Therefore, not only decomposition of target contaminant but also the comprehensive toxicity of oxidation intermediates should be regarded as index to evaluate a photocatalysis technology.

Visible-light-driven photo-Fenton reactions using Zn1-1.5xFexS/g-C3N4 photocatalyst: Degradation kinetics and mechanisms analysis

The visible-light responsive hybrid catalysts (Zn0.94Fe0.04S/g-C3N4 or ZCN) were synthesized by a rapid microwave hydrothermal method. Our results showed that the deposition of Fe-doped ZnS onto g-C3N4 sheets prevented the aggregation of Zn0.94Fe0.04S and increased the surface area for mass transfer and light absorption. The highest degradation rate of p-nitrophenol (PNP) was 96.0% and the total organic carbon removal rate was 55.4% after 60-min simulated solar light irradiation on ZCN with Fe doping and g-C3N4 loading ratios of 0.04 and 0.20, respectively. Hydroxyl radical played a dominant role in PNP degradation, which was primarily attributed to the photo-Fenton reactions. The PNP degradation pathway involved denitration and hydroxylation reactions according to the Density Function Theory calculations and HPLC-MS/MS results. The QSAR analysis indicated that the toxicity of most intermediates was lower than PNP. This study develops novel materials with superior photocatalytic activity for elimination of refractory organic pollutants in wastewater.

Insecticidal Activity of Chromobacterium phragmitis, a Recently Described Bacterium from Tidal Marshes

Several isolates of the recently described bacterial species Chromobacterium phragmitis Blackburn et al. were obtained from water collected from low-salinity tidal marshes in Maryland and Virginia. Bacteria were cultured in a liquid medium and applied to artificial diets in the laboratory. One of two Maryland isolates, IIBBL 113-1, was highly toxic to larvae of the cabbage looper Trichoplusia ni (Hübner) and the diamondback moth, Plutella xylostella (L.). The other Maryland isolate, IIBBL 112-1T, and the Virginia isolates were less toxic to these species. Maryland isolates were toxic to larvae of the seedcorn maggot Delia platura (Meigen), while a Virginia isolate, IIBBL 274-1, was of intermediate toxicity against D. platura. The C. phragmitis isolate IIBBL 113-1 was toxic to adults of the red flour beetle Tribolium castaneum (Herbst), while other C. phragmitis isolates had no activity against this species.

Synthesis and fouling resistance of capsaicin derivatives containing amide groups

Capsaicin, which inhibits the attachment and growth of fouling organisms, is a bioactive substance that is generally recognized as a highly active environmental algaecide agent. Its derivatives are simple in structure and have been proven to have low toxicity and be environmentally friendly. Six capsaicin derivatives were synthesized via Friedel-Crafts alkylation and characterized using melting point (MP) analysis, infrared (IR) spectroscopy, nuclear magnetic resonance (1H NMR) spectroscopy and high-resolution mass spectrometry (HRMS). The inhibition effect and toxicity of these compounds towards Phaeodactylum tricornutum (P. tricornutum), Skeletonema costatum (S. costatum) and Chaetoceros curvisetus (C. curvisetus) were tested. The capsaicin derivatives all showed inhibitory effects. In particular, compound E with over 95% (3 mg·L−1) inhibition and intermediate toxicity was superior to the other compounds, reflecting an environmentally friendly effect. This finding indicates that capsaicin derivatives possess the potential to become environmentally friendly algaecide agents. The fouling resistance of capsaicin derivatives incorporated into the coatings as antifouling agents was measured in the marine environment. The results showed that capsaicin derivatives possess excellent fouling resistance, with only a small amount of algae and muck attached to the tested panel at 90 days. The above results provide a scientific basis for the application of capsaicin derivatives as environmentally friendly antifouling agents.

Electrochemical Oxidation of Sulfonamides with Boron-Doped Diamond and Pt Anodes.

Electrochemical oxidation processes usually favored specific degradation pathways depending on anode materials. In this work, a series of sulfonamides (SNs) were degraded by electrochemical oxidation. Compared to Pt anodes (0.1567–0.1795 h−1), degradation rates of SNs were much higher at boron‐doped diamond (BDD) anodes (2.4290–13.1950 h−1). However, the same intermediates were detected in the two anode systems. Due to the strong oxidizing ability of BDD anodes, a large amount of intermediates with high toxicities were initially generated and then finally reduced in the BDD anode systems, while the amount of intermediates continuously increased in the Pt anode systems. Additionally, SNs were degraded faster in Na2SO4 than NaH2PO4 electrolytes at BDD anodes, while they were similar at Pt anodes. This study demonstrated that the degradation pathways of SNs at BDD and Pt anodes were similar, but the evolutions of intermediate amounts and toxicities were different due to their varied oxidizing abilities.

2D/1D graphitic carbon nitride/titanate nanotubes heterostructure for efficient photocatalysis of sulfamethazine under solar light: Catalytic “hot spots” at the rutile–anatase–titanate interfaces

2D/1D graphitic carbon nitride hybridized with titanate nanotubes (g-C3N4/TNTs) was prepared through a hydrothermal reaction–calcination method. The photocatalyst exhibited high degradation efficiency for sulfamethazine (SMT) through photocatalysis under simulated solar light. The optimized material was composed of anatase, rutile, titanate and g-C3N4 crystalline phases. In situ transformation of titanate to anatase and rutile with specific content proportion (∼80:20, P25-type composition) leaded to formation of nanoscale “hot spots” at rutile–anatase–titanate interfaces, and then subsequent charge transfer occurred. Large specific surface area of TNTs as skeleton resulted in high-efficient interface reaction, while heterojunction with g-C3N4 further extended the adsorption to visible light region and retarded electron-hole pairs recombination. Density functional theory (DFT) calculation indicated the SMT sites with high Fukui nucleophilic (f-) index prefered to be attacked by radacils. Reduced toxicity of SMT degradation intermediates, good reusability and stability of g-C3N4/TNTs all suggested the great application potential in practical water treatment area.

Photocatalytic activity of N-TiO2/O-doped N vacancy g-C3N4 and the intermediates toxicity evaluation under tetracycline hydrochloride and Cr(VI) coexistence environment

In this study, N-TiO2/O-doped N vacancy g-C3N4 was synthesized by the solvothermal method. The optimized photocatalyst N-TiO2/CNONV-2 has excellent photocatalytic activity, and it can reach about 3 times of tetracycline hydrochloride (TC−HCl) degradation rate and 41 times of Cr(VI) reduction rate comparing with N vacancy g-C3N4. Meanwhile, N-TiO2/CNONV-2 exhibited excellent photocatalytic activity and chemical stability under TC−HCl and Cr(VI) coexistence environment. The enhancement photocatalytic activity mechanism of N-TiO2/CNONV-2 is that Z-scheme heterojunctions accelerate the separation of electrons and holes, while mainly O2– and h+ attack TC−HCl and e– reduces Cr(VI) under TC−HCl and Cr(VI) coexistence environment. The influence of environmental factors (pH, organic matter, and inorganic salt) on the photocatalytic activity of N-TiO2/CNONV-2 under TC−HCl and Cr(VI) coexistence environment was studied. Furthermore, the toxicity of the intermediates was evaluated by quantitative structure-activity relationship (QSAR) prediction. The results demonstrated that the toxicity of TC intermediates can be degraded into low level over N-TiO2/CNONV-2.

Potential impacts of lanthanum and yttrium through embryotoxicity assays with Crassostrea gigas

Abstract In the last decades, the production of electronic devices, which relies on rare earth elements (REE) such as yttrium (Y) and lanthanum (La), has increased exponentially, a pattern that should continue in the future. Besides the lack of raw materials, the growing generation of electronic waste (E-waste) and the REEs direct or indirect discharge into the environment raises worldwide concern. Mostly, given the scarcity of data about their toxicity to marine biota. In this study, a standardized toxicity test on oyster Crassostrea gigas embryonic development was performed to assess the impacts of La and Y. Lanthanum exerted significantly higher toxicity than Y, with median effect dose concentrations (EC50) of 6.7 to 36.1 µg L−1 (24 and 48 h) for La; and 147 to 221.9 µg L−1 (24 and 48 h) for Y. Higher toxicity of La was likely related to higher bioavailability of free ionic form (La3+). Comparison of toxicity thresholds with literature indicated that La is among the most toxic compounds to C. gigas embryos, while Y was ranked among compounds with intermediate toxicity. Overall, this work brings new insights into the potential implications of the widespread use of high-tech products, if appropriate management measures are not taken.

Dramatic enhancement effects of l-cysteine on the degradation of sulfadiazine in Fe3+/CaO2 system

Excessive sulfonamides accumulated in soil and groundwater seriously menace the ecological environment and human health. The performance of a Fenton-like system applying Fe3+ and calcium peroxide (CaO2) in the presence of l-cysteine(l-cys) for sulfadiazine (SDZ) degradation was investigated. Compared with other chelating agents such as citric acid, butyric acid and Ethylenediaminetetraacetic acid, l-cys could effectively promote the SDZ removal in Fe3+/CaO2 system. With the addition of 0.5 mM l-cys, the SDZ degradation increased from 2.14% to 66.53% in 60 min. High concentration of HCO3− inhibited the degradation of SDZ while slightly negative effects on SDZ degradation were observed in the presence of Cl− or humic acid (HA) in l-cys/Fe3+/CaO2 system. Electron paramagnetic resonance (EPR) analysis and radicals scavenge tests affirmed the generation of OH and O2- in l-cys/Fe3+/CaO2 system. Possible degradation pathway of SDZ was speculated and the toxicity of SDZ intermediates was further evaluated. l-cys could enhance the reduction of Fe3+ to Fe2+ and reduced the Fe3+ precipitation due to the l-cys could form stable complexes with Fe3+. l-cys/Fe3+/CaO2 system exhibited high mineralization ability. Overall, these results indicated that l-cys is a promising chelating agent for sulfadiazine wastewater treatment.

Photocatalytic degradation of norfloxacin using N-doped TiO2: Optimization, mechanism, identification of intermediates and toxicity evaluation

In this study, the photocatalytic degradation of Norfloxacin (NOR) has been studied using N-doped TiO2 (N–TiO2) under visible light irradiation, which was synthesized from a self-owned patent recipe and procedure. Subsequently, a three-factor five-level model, which was based on the central composite design (CCD), was developed to determine the optimal NOR concentration, N–TiO2 dosage, and initial pH in practical use. Meanwhile, the degradation pathway was identified by high-performance liquid chromatography-mass spectroscopy (HPLC-MS). Moreover, the toxicity of degradation intermediates was determined using the bacterium Escherichia coli so as to evaluate the health risk of the photocatalytic treated influent. The synthesized N–TiO2 nanoparticles were spherical, and the grain sizes were distributed from approximately 12 nm–20 nm, with a specific surface area of 148.52 m2/g. The light absorption is range from the ultraviolet region to the visible light region since the band gap was reduced to 2.92eV. It was demonstrated from the response surface method results that the initial NOR of 6.03 mg/L, N–TiO2 dose of 0.54 g/L, and pH of 6.37 could be the proposed optimal degradation conditions, which resulted in a 99.53% removal of NOR within 30 min under visible light irradiation. Two possible degradation pathways were proposed, including the replacement of F atoms by hydroxyl radicals, piperazinyl ring cleavage, hydroxylation, and decarboxylation. In the acute toxicity test, the toxicity declined 55% after photocatalytic treatment for 60 min. The results show the feasibility and novelty for photocatalytic treatment of antibiotics by N–TiO2 photocatalyst.

Trace amounts of fenofibrate acid sensitize the photodegradation of bezafibrate in effluents: Mechanisms, degradation pathways, and toxicity evaluation

Effluent organic matter (EfOM), which is composed of background natural organic matter (NOM), soluble microbial degradation products, and trace amounts of organic pollutants, can play an important role in the photodegradation of emerging pollutants in the effluent. In this study, the impact of organic pollutants, using fenofibrate acid (FNFA) as a representative, on the photodegradation of emerging contaminants, using bezafibrate (BZF) as a representative, in effluents was investigated. It is found that BZF undergo fast degradation in the presence of FNFA although BZF is recalcitrant to degradation under simulated sunlight irradiation. The promotional effect of FNFA is due to the generation of singlet oxygen (1O2) and hydrated electrons (e-aq). Based on the structures of the identified intermediates, 1O2 initiated oxidation and e-aq initiated reduction reactions were the main photodegradation pathways of BZF in the effluents. The toxicity of the main photodegradation intermediates for BZF and FNFA was higher than that of the parent compounds, and the acute toxicity increased during simulated sunlight irradiation. The results demonstrated that trace amounts of organic compounds in EfOM can play an important role in sensitizing the photodegradation of some emerging pollutants in the effluent.

Highly active WO3@anatase-SiO2 aerogel for solar-light-driven phenanthrene degradation: Mechanism insight and toxicity assessment

The global energy crisis and water pollution drive the researchers to develop highly effective and less energy intensive water purification technologies. In this study, a highly active WO3@TiO2–SiO2 nanocomposite was synthesized and used for photocatalytic degradation of persistent organic pollutants under simulated solar light. The optimum WO3@TiO2–SiO2 prepared with 2 wt% WO3 loading and calcination at 800 °C exhibited higher photocatalytic activity, as the rate constant (k1) for phenanthrene degradation was ∼7.1 times of that for the commercial TiO2 (P25). The extremely large specific surface area (>400 m2/g) of WO3@TiO2–SiO2 afforded it with enlarged pollutants adsorption performance and abundant active surface sites. The heterojunction of anatase with SiO2 as well as loading of WO3 decreased the band gap energy (Eg) of TiO2, which extended the utilization spectrum of TiO2 to visible region. Formation of Ti–O–Si band indicated the excess charges can cause Brønsted acidity due to the absorption of protons to compensate the charges. Moreover, the migration of photo-excited electrons from the conduction band of anatase to WO3 and holes in the opposite direction restrained the electron-hole recombination. The photocatalytic degradation mechanism and pathway for phenanthrene degradation were proposed based on experimental analysis and density functional theory (DFT) calculation, and the toxicities of the degradation intermediates were evaluated by quantitative structure–activity relationship (QSAR) analysis. WO3@TiO2–SiO2 also showed good separation (settling) performance and high stability. Our work is expected to offer new insight into the photocatalytic mechanism for WO3, TiO2 and SiO2 based heterojunctions, and rational design and synthesis of highly efficient photocatalysts for environmental application.

Oxidation degradation of tris-(2-chloroisopropyl) phosphate by ultraviolet driven sulfate radical: Mechanisms and toxicology assessment of degradation intermediates using flow cytometry analyses

Organophosphate flame retardants (OPFRs) were frequently detected in biotic and abiotic matrix owing to their persistence and recalcitrant degradation. Some specific OPFRs, such as tris-(2-chloroisopropyl) phosphate (TCPP), pose a significant potential risk to human health due to their high water solubility. Therefore, an environmentally sound and high efficient technique is in urgent need of controlling TCPP. This research is focused on degrading TCPP using ultraviolet-persulfate (UV/PS) technique. The degradation reaction of TCPP followed a pseudo-first order kinetics with an apparent rate constant (kobs) at 0.1653 min−1. As the photocatalytic reaction proceeded, TCPP was transformed to twelve degradation intermediates via the selective electron-transfer reactions induced by activated sulfate radical. Anions existence and pH value significantly inhibited the degradation efficiency, implying that it was hard for TCPP to reach up to complete mineralization in actual water treatment process. Additionally, toxicological assessment of degradation intermediate mixture was conducted using Flow cytometry (FCM) analyses, and the result showed that the intracellular reactive oxygen species (ROS) and cell apoptotic rates significantly declined, and membrane potential (MP) increased in comparison with original TCPP. On the other hand, the negative impacts of these degradation products on DNA biosynthesis in Escherichia coli were weakened based on cell cycle analysis, all of which indicated that toxicity of these degradation intermediates was obviously reduced via UV/PS treatment. To summarize, an appropriate mineralization is effective for TCPP detoxification, suggesting the feasibility of TCPP control using UV/PS treatment in water matrix.

Transformation pathway and toxicity assessment of malathion in aqueous solution during UV photolysis and photocatalysis

In drinking water treatment, complete mineralization of organophosphorus pesticides (OPPs) by UV-based advanced oxidation processes (UV AOPs) is rarely achieved. The formation of intermediate oxidation byproducts would likely have some profound effects on toxicity of the reaction solutions. This study investigated the intermediate oxidation byproducts, transformation pathway and toxicity of malathion solutions during the treatment processes of UV alone, UV/H2O2, UV/TiO2 and UV/Fenton. The main intermediate oxidation byproducts were derived using ultra-performance liquid chromatography - electrospray - time-of-flight mass spectrometry. Thereby the transformation pathway for each of these treatment processes was proposed. The results indicate that in UV photolysis, the transformation pathway of malathion proceeded initially via cleavage of the phosphorus-sulfur bonds while in photocatalysis, the desulfurization from a PS bond to a PO bond was the primary degradation pathway. Interestingly, only in the UV/TiO2 process a small fraction of malathion was found decomposed via a demethylation reaction. At the same time, a toxicity assessment of the treated solutions was conducted by both luminescence inhibition of Vibrio fischeri and inhibition of acetylcholinesterase (AChE). It was found that after UV AOP treatment, the toxicity of the malathion aqueous solution increased sharply. In contrast, no increase in toxicity was observed for the malathion aqueous solution after UV alone treatment. This study demonstrates that the high removal efficiency achieved by OPPs does not imply that detoxification of the water solution has been achieved. On the contrary, the toxicity of the treated solutions by OPPs may be increased significantly depending on the selected treatment processes.

Insights into a CQD-SnNb2O6/BiOCl Z-scheme system for the degradation of benzocaine: Influence factors, intermediate toxicity and photocatalytic mechanism

The development of a novel Z-scheme system with a high separation efficiency of the charge carriers for remarkably enhanced photocatalytic activity is highly desirable. Herein, a carbon quantum dot-modified SnNb2O6/BiOCl (CQD-SNO/BOC) Z-scheme system, in which the CQDs acted as a bridge for the charge carriers, was successfully synthesized. As expected, the CQDs acted as a bridge for the charge carriers that could separate and accumulate electrons from SnNb2O6 and holes from BiOCl by promoting the transfer of the photoinduced charge carriers, which enabled the BiOCl holes to maintain their high oxidation capability. Additionally, the CQDs not only endowed the SNO/BOC Z-scheme system with a large specific surface area that provided a greater number of active sites but also noticeably improved its visible light absorption capacity. Therefore, the CQD-SNO/BOC Z-scheme system showed an improved photocatalytic performance for the degradation of benzocaine (BC), which was over 20 times, 10 times and 2 times greater than those of BiOCl, SnNb2O6 and SNO/BOC Z-scheme systems, respectively. In addition, the effects of catalyst concentration, pH value, different anions, and humic acid (HA) concentration on the photodegradation of BC were investigated in depth. Simultaneously, a four-stage pathway for the degradation of BC was proposed based on the degradation products that were identified, and the accuracy of this pathway was further verified based on biotoxicity assessments and toxicity predictions of the products. According to the ESR spectra and active species trapping experiments, a mechanism for the CQD-SNO/BOC Z-scheme system was proposed, in which the CQD bridge accelerated charge transfer. Based on these results, the CQD-modified Z-scheme system could be an efficient and promising photocatalyst for the degradation of PPCPs in water.

Heterogeneous photocatalytic degradation of diuron on zinc oxide: Influence of surface-dependent adsorption on kinetics, degradation pathway, and toxicity of intermediates

Heterogeneous photocatalytic reaction has been generally applied for degradation of toxic contaminants. Degradations of a compound using the same kind of catalyst that was synthesized differently are commonly found in literature. However, the reported degradation intermediates are normally inconsistent. This issue is especially important for the degradation of toxic compounds because intermediates may be more toxic than their parent compounds and understanding the reason is necessary if appropriate catalysts are to be designed. This work systematically compares the photocatalytic degradation of diuron, a toxic recalcitrant herbicide, on two forms of zinc oxide (ZnO), i.e., conventional particles with zinc- and oxygen-terminated polar surfaces as the dominating planes, and nanorods with mixed-terminated nonpolar surfaces. Experimental and theoretical results indicate that both the rate of reaction and the degradation pathway depend on the adsorption configuration of diuron onto the surface. Diuron molecules adsorb in different alignments on the two surfaces, contributing to the formation of different degradation intermediates. Both the aliphatic and aromatic sides of diuron adsorb on the polar surfaces simultaneously, leading to an attack by hydroxyl radicals from both ends. On the other hand, on the mixed-terminated surface, only the aliphatic part adsorbs and is degraded. The exposed surface is therefore the key factor controlling the degradation pathway. For diuron degradation on ZnO, a catalyst confined to mixed-terminated surfaces, i.e., ZnO nanorods, is more desirable, as it avoids the formation of intermediates with potent phytotoxicity and cytogenotoxicity.

Derivation of internal dose-based thresholds of toxicological concern for occupational inhalation exposure to systemically acting organic chemicals

This study aimed at deriving occupational thresholds of toxicological concern for inhalation exposure to systemically-acting organic chemicals using predicted internal doses. The latter were also used to evaluate the quantitative relationship between occupational exposure limit and internal dose. Three internal dose measures were identified for investigation: (i) the daily area under the venous blood concentration vs. time curve, (ii) the daily rate of the amount of parent chemical metabolized, and (iii) the maximum venous blood concentration at the end of an 8-hr work shift. A dataset of 276 organic chemicals with 8-hr threshold limit values-time-weighted average was compiled along with their molecular structure and Cramer classes (Class I: low toxicity, Class II: intermediate toxicity, Class III: suggestive of significant toxicity). Using a human physiologically-based pharmacokinetic model, the three identified dose metrics were predicted for an 8-hr occupational inhalation exposure to the threshold limit value for each chemical. Distributional analyses of the predicted dose metrics were performed to identify the percentile values corresponding to the occupational thresholds of toxicological concern. Also, simple linear regression analyses were performed to evaluate the relationship between the 8-hr threshold limit value and each of the predicted dose metrics, respectively. No threshold of toxicological concern could be derived for class II due to few chemicals. Based on the daily rate of the amount of parent chemical metabolized, the proposed internal dose-based occupational thresholds of toxicological concern were 5.61 × 10−2 and 9 × 10−4 mmol/d at the 10th percentile level for classes I and III, respectively, while they were 4.55 × 10−1 and 8.5 × 10−3 mmol/d at the 25th percentile level. Even though high and significant correlations were observed between the 8-hr threshold limit values and the predicted dose metrics, the one with the rate of the amount of chemical metabolized was remarkable regardless of the Cramer class (r2 = 0.81; n = 276). The proposed internal dose-based occupational thresholds of toxicological concern are potentially useful for screening-level assessments as well as prioritization within an integrated occupational risk assessment framework.

AgI loading BiOI composites with enhanced photodegradation efficiency for bisphenol A under simulated solar light

Bismuth oxyiodide (BiOI) is a narrow band gap semiconductor which can be driven by visible irradiation. In order to efficiently separate photo-generated carriers and utilization of visible light, a facile solvothermal approach was used to synthesize a novel AgI loading BiOI 3D hierarchical composite (AgI-BiOI). The AgI-BiOI with Ag and Bi molar ratio of 1:8 (AgI-BiOI (1–8)) showed great enhancement for photocatalytic degradation of bisphenol A (BPA) with pseudo-first degradation rate constant about 3.7 or 14.5 times than that of pristine BiOI or AgI under simulated solar light. This synergistic enhancement for BPA degradation on AgI-BiOI(1–8) is mainly ascribed to enhancing the light absorption intensity and accelerating photo-generated carriers separation due to the formation of AgI-BiOI heterojunction. Free radical quenching experiments proved that positive holes (h+) and superoxide (O2•−) radicals were dominantly responsible for the degradation of BPA rather than singlet oxygen (1O2) or hydroxyl radicals (•OH). The AgI-BiOI(1–8) hardly showed any ecotoxicity to C. elegans through lethal experiments. The luminance bacteria acute toxicity of degradation intermediates of BPA increased before 30 min then reduced significantly with reaction. The good durability and environmental-friendly characteristics make AgI-BiOI(1–8) catalyst to be a good solar light-driven candidate.

A cell-free platform for the prenylation of natural products and application to cannabinoid production

Prenylation of natural compounds adds structural diversity, alters biological activity, and enhances therapeutic potential. Because prenylated compounds often have a low natural abundance, alternative production methods are needed. Metabolic engineering enables natural product biosynthesis from inexpensive biomass, but is limited by the complexity of secondary metabolite pathways, intermediate and product toxicities, and substrate accessibility. Alternatively, enzyme catalyzed prenyl transfer provides excellent regio- and stereo-specificity, but requires expensive isoprenyl pyrophosphate substrates. Here we develop a flexible cell-free enzymatic prenylating system that generates isoprenyl pyrophosphate substrates from glucose to prenylate an array of natural products. The system provides an efficient route to cannabinoid precursors cannabigerolic acid (CBGA) and cannabigerovarinic acid (CBGVA) at >1 g/L, and a single enzymatic step converts the precursors into cannabidiolic acid (CBDA) and cannabidivarinic acid (CBDVA). Cell-free methods may provide a powerful alternative to metabolic engineering for chemicals that are hard to produce in living organisms.

Repurposing peroxisomes for microbial synthesis for biomolecules.

Microbial synthesis represents an alternative approach for the sustainable production of chemicals, fuels, and medicines. However, construction of biosynthetic pathways always suffers from side reactions, toxicity of intermediates, or low efficiency of substrate channeling. Subcellular compartmentalization may contribute to a more efficient production of target products by reducing side reactions and toxic effects within a compact insular space. The peroxisome, a type of organelle that is involved in catabolism of fatty acids and reactive oxygen species, has attracted a great deal of attention in the construction of eukaryotic cell factories with little impact on essential cellular function. In this chapter, we will systematically review recent advances in peroxisomal compartmentalization for microbial production of valuable biomolecules. Additionally, detailed experimental designs and protocols are also described. We hope a comprehensive understanding of peroxisomes will promote their application in metabolic engineering and synthetic biology.